Coded track circuit for railroads



May 7, 1946. F. X. REES CODED TRACK CIRCUIT FOR RAILROADS Filed NOV. 19, 1942 4 Sheets-Sheet l owou 3.62:

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May 7, 1946. F. x. REES CODED TRACKGIRCUIT FOR RAILROAD-S 4 Sheets-Sheet Filed NOV. 19,. 1942 INVENTOR May 7, 1946. F. x. REES CODED TRACK CIRCUIT FOR RAILROADS Filed Nov. 19, 1942 4 Sheets-Sheet 4 INVE n59 BY 4-,, ATTORNEYY Patented May 7, 1946 UNITED STATES PATENT OFFICE 2,399,760 CODED TRACK CIRCUIT FOR RAILROADS Frank X. Rees, Rochester, N. Y., assignor to Genirai Railway Signal Company, Rochester,

Application November 19, 1942, Serial No. 466,151

20 Claims.

The present invention relates to automatic block signalling systems for railroads, and more particularly pertains to the improvement of coded track circuits used in such signalling systems. The conventional coded track circuit provides that impulses of current are successively applied to one end of a track circuit section with spaced intervals conveniently termed off periods to comprise a driven code, the impulses of which are applied at selected rates in accordance with traffic conditions of an adjacent track section. At the opposite end of the track circuit section, a code following track relay is connected across the track rails to receive the driven code impulses and act upon suitable code responsive means that decodes such impulses in accordance'with their rate for distinctively controlling the indications of a signal governing traflic into that track circuit section without the use of any line Wires.

Such a coded track circuit may also be organized to have an inverse code transmitted in a direction over the track circuit section opposite to the direction of the transmission of the driven code by impressing impulse upon the track circuit during the off periods of the driven code at-the end of the track circuit which is receiving such driven code. Then a code following track relay is employed to receive the inverse code impulses at the end of the track circuit transmitting the driven code which relay also acts upon suitable decoding means.

In my prior patent No. 2,353,930 granted July 18, 1944, I provided a coded track circuit signalling system of the type described generally above, and in which each impulse of the driven codes as Well as each impulse of the inverse codes comprised a series of alternating current halfcycles. In other words, each code impulse was disclosed as being a series of pulses of the same polarity. In various other systems of the conventional coded track circuit type, the code impulses are of steady direct current of the same polarity. It has been found, that, when such systems as mentioned above, are applied to certain sections of trackway, a characteristic is present which has been conveniently termed the storage battery effect. In brief, when an impulse is applied at one end of the track circuit, that impulse energizes the track relay at the opposite end of the track circuit and also act to charge, so to speak, the track rails in combina tion with the ballast conditions in such a Way that when the impuls i removed at the transmitting end, there is a tendency for the relay to bemaintained energized due to the charge placed in the track circuit during the application of such impulse. In some cases, the effect may be so pronounced, that the charge will build up over a period of time by the application of a succession of impulses of the same polarity until it has a substantial effect on the code following track relay. Such a storage battery effect varies with different ballast conditions and also varies in accordance with the Wet and dry conditions of the ballast of any given track circuit, and thus makes it difficult with adverse ballast conditions to ob tain uniform operation of track relays in response to a code. Thus, the decoding apparatus distinctively responsive to different code rates must be tuned rather broadly so as to allow for such variations.

In accordance with the present invention, it is proposed to organize a coded track circuit in a manner to eliminate the storage battery effect by causing the track relay to be positively driven by positive and negative impulse energy to its opposite positions. This prevents a charge from building up in the track circuit, as each impulse serves to cancel the charging eifect of the preceding impulse. Also, such an organization permits sharper tuning of the decoding apparatus and still maintains its reliable operation under varying ballast conditions. It also permits the adjustment of the coded track circuit for lower ballast conditions and thus permits faster coding operation for even adverse ballast conditions.

A further feature of the present invention is to provide that the driven code impulses shall be of very short duration, merely of suilicient duration to cause the proper amount of energyto be impressed upon the track circuit to efiect the proper operation of the code following track relay at the opposite end, and this value remains substantially constant regardless of the code rate employed at any particular time. In brief, a code period actually includes two pulses of current, one pulse for operating the track relay to one position and another pulse for operating it to the opposite position. However, both of these short impulses combined are of much shorter duration than the usual driven code pulse having of a period of duration in accordance with the rate of code then being applied. In this way, the present invention accomplishes a substantial saving in energy.

In accordance with the present invention, the inverse codes are transmitted in the same manner as the driven codes, namely, by the transmission of positive and negative impulses between the impulses of the driven code to thereby operate the inverse code receiving track relay to its opposite positions by short pulses of opposite polarities. This organization providing for very short driven and inverse code pulses permits the use of higher code rates for the driven code and still maintains proper transmission of the inverse code.

A further feature of the present invention is that the use of foreshortened driven and inverse code pulses permits the repeating of these pulses past a cut-section in the usual block without the formerly required decoding apparatus. This is a substantial saving and therefore makes the system of the present invention more economical in its application.

With the inverse code organized to have pulses of opposite polarities to drive its code receiving track relay to opposite positions, an inherent check is provided against what has been termed self-coding in the presence of stra direct currents on the track circuit. This will be understood by considering the usual coded track circuit where the inverse code receiving track relay and the source of energy at the driven code transmitting end are alternately placed across the track circuit by a code transmitting relay. While the code transmitting relay is in operation, a stray potential across the track rails would cause the inverse code receiving track relay of the usual biased to one position type to be intermittently energized thereby simulating a regular inverse code. But it can be seen the mag-stick type relay of the present invention would require that the stray potential have reversed polarities for the successive impulses in order to effect any harmful results. This of course is not characteristic of a stray potential, and hence in the present invention, the inverse code receiving relay is operated to one position and remains in that position regardless of the continued operation of the driven code transmitting relay.

Another feature of the present invention is to employ an impulse repeating relay associated with the code transmitting contacts for both the driven and inverse codes so organized that this impulse repeating relay determines the length of each driven or inverse code pulse as the case may be in accordance with the strength of the source supplying such energy. Thus, if the source of energy is above normal potential, the impulse will be slightly shortened; while if the source of energy is somewhat weaker than normal, the impulse period is lengthened in accordance therewith. This provides a more positive operation of the code following track relay at the opposite end of the track circuit.

Another feature in connection with this impulse repeating or timing relay, is that it is arranged to be isolated from the track circuit after it has repeated an impulse in a manner so as to be unresponsive to the application of an impulse at the opposite end of the track circuit. This is especially desirable so that the application of a driven or inverse code pulse will not effect the operation of this relay and thereby cause erroneous conditions in the track circuit, and also to provide that the relay shall be normally deenergized to effect economy in the energy consumption of the system.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings, and in part pointed out as the description of the invention progresses.

In describing the invention in detail, reference will be made to the accompanying drawings in which like letter reference characters provided with distinctive numerals designate corresponding parts throughout the several views, and in which:

Fig. 1 illustrates a track circuit section having a coded track circuit organization employing alternating current in accordance with the principles of the present invention, which coded track circuit section is a portion of a signalling system for governing trailic in one direction with approach lighting for the associated signals;

Fig. 2 illustrates diagrammatically various conditions of energization of relays and the position of their contacts for one particular rate of coding in a track circuit organized in accordance with the present invention as disclosed in Fig. 1;

Fig. 3 illustrates a track circuit section having a coded track circuit organization employing direct current in accordance with the principles of the present invention, which coded track circuit section is a portion of a signalling system for governing trafiic in one direction with approach lighting control for the associated signals;

Fig. 4 is one modified form of the invention disclosed in Fig. 3; and

Fig. 5 is another modified form of the invention disclosed in Fig. 3.

For the purpose of simplifying the illustrations and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammaticall and certain conventional illustrations have been employed, the drawings having been made more with the purpose of making it easy to understand the principles and mode of operation than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a conventional manner, and symbols are used to indicate connections to the terminals of batteries or other sources of electric current instead of showing all of the wiring connections to these terminals.

The symbols (-1-) and are employed to indicate the positive and negative terminals respectively of suitable batteries or other suitable sources of direct current; and the circuits with which these symbols are employed always have current flowing in the same direction. In the drawings where an alternating current supply is required, the terminals supplied with such alternating current have the legend AC supply associated therewith.

With reference to Fig. 1 of the accompanying drawings, a stretch of track has been divided into track sections by suitable insulated joints forming the track sections 3T, 3-2'1" and 2T. A signal 2, disclosed as being of the color light type, is provided for governing the entrance of traflic into the track section 32T; and similarly, a signal 3 is provided at the exit end of the track circuit 32T for governing the entrance of traffic into the track section 3T. These signals could of course be of any other suitable type if desired.

At the exit end of the track circuit 3--2T, are located suitable coding contacts designated lBflCT and T which are operating at a code rate and a '75 code rate respectively. These coding contacts act through rectifier units 10 and H to operate a code transmitting relay 3C]? to its opposite positions in accordance with the 180 code rate or the 75 code rate depending upon whether front contact l2 of a home relay 3H is closed or whether the back contact l2 of such relay is closed. It is of course understood that the relay 3H and its associated distant e ay 3D are selectivcly controlled in accordance with the codes received over the track section 3T in a similar manner as illustrated in detail for the home and distant relays 2H and 2D associated with the signal 2 and track section 3-2T.

The transmitting relay 3GP and its associated timing relay SCPT act to apply pulses of opposite polarity formed by half-cycles of alternating current to the track circuit 3-2T to comprise a driven code as will be explained in detail hereinafter.

At the opposite end of the track circuit 3.-2T, a track relay ZTR is responsive to the driven code pulses and this relay acts through its repeater relay ZTRP on the decoding apparatus comprising a decoding transformer, rectifier contacts on relay 2 i P, condensers and asymmetrical units to decode the codes in the usual way, so as to pick up the relay 2H upon the reception of a driven code of any code rate but it energized only upon the reception of a code of the 180 code rate.

Associated with the track relay 2TB. is a code transmitting relay 2GP. Both of the relays ZTRP and 2GP are controlled through rectifier units l3 and M in accordance with the position of contact l5 of the track relay ZTR; and the relay 2GP acts to cause the transmission of inverse code pulses over the track circuit, which impulses are received by the track relay 3TH at the opposite end of the track circuit. The operation of relay 3TH. by inverse code pulses is decoded by front contact repeater relay 3FP and frontback contact repeater relay 3F'BP as will be pointed out in detail later. A relay ZCPT is associated with the transmitting relay ZCP for performing certain timing operations which will be hereinafter described in detail.

It may be noted that all of the transmitting relays CP, transmitting timing relays CPT, track relays TR and their repeater relays TRP are of the so-called mag-stick type, that is, such relays are of the polarized type and their contacts are actuated to one position or the other in accordance with the polarity of energization of such relays, and their contacts remain in the last actuated position although deenergized until such relay is again energized with the opposite polarity.

It is believed that further features of the invention will be best understood by considering the detailed operation.

Operation.-Withreference to Fig. 1, it will be seen that the coding contact I 800T is in a lefthand position and front contact I2 of relay 3H is closed, which permits a series of positive halfincludes the rectifier unit I O which for convenience has been designated a positive rectifier to indicate that it will pass halfcycles of alternating current when the right-hand terminal of the associated transformer l6 has a positive instantaneous relative polarity.

With contact ll of relay 3GP in a left-hand position, it is seen that positive half-cycles of alternating current from the secondary of transformer l8 cannot pass through the positive rectifier It] to the track rails of section 3-.-2 'I because contact 20 0f the relay 3CPT is in a lefthand position. This is because relay 3CPT is ener ized with positive half-cycles of alternating current from the transformer l8 through contact I! of relay 3GP in a left-hand position, positive rectifier 2|, lower windings of relay 3CPT, to the right-hand terminal of transformer 18.

At the right-hand end of the track section 3- -2T, positive half-cycles of alternating current are passing from the secondary of transformer 24 through the rectifier l3 and contact I5 of the track relay 2TB, in a left-hand position through both the transmitting relay 2GP and the track repeating relay Z'IRP in multiple, so that the contacts of both these relays are actuated to right-hand positions.

With contact 25 of relay 2GP in a right-hand position, it will be seen that positive half-cycle of alternating current from the transformer 25 can pass through the rectifier unit 2'! and the relay 2CPT to actuate its contacts to right-hand positions. However, with contact 28 in a righthand position such positive half-cycles from the transformer 26 cannot pass to the track section 3-2T.

In brief, the conditions indicated in the drawings represent the condition of the apparatus after a positive driven code pulse has been transmitted to the right over the upper rail of the track section 3--2T followed by the transmission of a positive inverse code pulse transmitted to the left over the upper rail of the track section 3-2T. Such positive inverse code pulse having passed through the track relay 3TH, leaves its contact 29 in a right-hand position in which its repeating relay 3FBP is energized by a circuit including contact 30 of relay 3FP. Assuming that the track relay 3TB is operated to its opposite positions in one position longer than the usual time space between impulses for the slowest code rate, then the relay 3FBP drops away and closes its back contact 3| to cause the illumination of signal 3 in accordance with the position of its home away opening contact 30 to cause the deenergization of relay 3FBP.

The relays 3H and 3D associated with the signal 3 are controlled in accordance with the reception of driven codes over the track section 3T in the same way as shown for the relays 2H and 2D associated with the signal 2, and presently to be described in further detail.

Let us assume that the movable contact of the coding contacts IBOCT moves to its right-hand position at the end of the measured period, then a circuit is made up for the relay 3GP including front contact 12 and the negative rectifier l I so that negative half-cycles of alternating current pass through the relay 3GP for the predetermined period measured by the coding contacts IBOCT. The first negative half-cycle of alternating current to pass through the relay 3GP causes the contacts of the relay 3GP to shift during the following positive half-cycle of alternating current as indicated in connection with its contact response in Fig. 2 of the accompanyin drawings. This shift during the succeeding positlve half-cycle of alternating current during which current cannot flow to'the track circuit through the circuits then made up, is due to the inherent lag in the relay 3GP, the relay being designed to have the proper characteristics to accomplish this. Thus, the contact shift is effected during the absence of current flow. Such features have been described more in detail in my prior application Ser. No. 462,225 filed October 16, 1942, now Patent No. 2,366,988 dated January 9, 1945, and no claim is made herein to subject matter common with such prior disclosure.

When contact I! of relay 3GP assumes its right-hand position during the positive half-cycle of alternating current, current cannot flow through the negative rectifier 33 nor through the negative rectifier 34. Thus, during the next succeeding negative half-cycle, current is supplied to the track section 3--2T from the secondary of transformer [8 through contacts H and 20 in out of correspondence positions and through the negative rectifier 33 and adjustable resistor unit 22. At the same time, the negative current flows through the relay 3CPT as indicated in Fig. 2, but the contact response for this relay SCPT is during the following positive half-wave of alternating current. This is because of the inherent delay characteristics of the relay 3CPT, the same as mentioned in connection with the relay 3GP. Thus, the contacts 20 of relay 3CPT shifts to the right while there is no current flow to the track circuit.

Inasmuch as the contact 20 shifts to the right during the positive half-wave of alternating current following the negative half-wave applied to the track circuit, only one negative half-wave of alternating current is impressed in the track rails indicated in Fig. 2 as a negative driven code pulse.

The reception of the negative driven code pulse over the track section 3-21 at the right-hand end of the track. circuit energizes the track relay 2TB through contact 35 of relay 2GP in a righthand position and contact 36 of relay 2CPT in a right-hand position. This negative energization of the track relay 2TB. causes its contact l to shift to a right-hand position during the following positivehalf-cycle of alternating current, as indicated in the drawing of Fig, 2 so that upon the succeeding negative half-cycle period, energy is supplied to the relay 2GP through negative rectifier unit M with contact IS in a righthand position. This shifts the contacts 25 and 35 of the the next succeeding positive half-cycle of alternating current. In other words, the negative half-wave energizes the relay 2GP, but its contacts do not assume the new positions until the following positive half-wave period (see Fig. 2).

Upon the next succeeding negative half-cycle period, current flows from the secondary of the transformer 25 through contact 25 in a left-hand position, negative rectifier unit 31, and contact 28 of relay .ECPT in a right-hand position, variable resistor 23, over the track section 3-2T to energize the track relay 3TB by reason of contacts 38 and 39 of relays 3GP and 3CPT being in corresponding right-hand positions. This negative inverse code pulse flowing through the inverse code track relay 3TB, actuates its contact 29 to a left-hand position during the succeeding positive alternating current half-cycle period as indicated in the diagrams of Fig. 2.

At the same time, a negative half-cycle of alterrelay 2GP to left-hand positions during nating current is caused to flow through contact 25 of relay 2GP from the secondary of transformer 26, negative rectifier unit 4|, and the upper winding of relay 2CPT so that it shifts its contacts 28 and 36 to left-hand positions during the succeeding positive period of the alternating current as indicated in the diagrams of Fig. 2. Thus, only a single half-cycle of alternating current is applied to the track section 3-2T to comprise the negative inverse code pulse, although a series of such negative half-cycles is applied to the relay ZCPT,

When the coding contact |CT has kept its movable contact in a right-hand position for a proper period of time, it again operates to the left causing the contacts of relay 3GP to be actuated by positive half-cycles of alternating current to left-hand positions. With contacts I! and 2B in non-corresponding positions, a, positive half-cycle of alternating current is supplied from the transformer l8 through the positive rectifier l9, and a variable resistor 22 to the track circuit 3--2T. This positive half-cycle of alternating current flows through the contacts 35 and 36 in left-hand positions so as to energize the relay 2TB in a direction to actuate its contact l5 to the left (see Fig. 2). The relay 3CPT is of course actuated by positive half-cycles of alternating current supplied from transformer l8 through contact I? in a left-hand position and positve rectifier 2! so that the polar contact 20 of relay BCPT is actuated to the left to allow only one half-cycle of alternating current to be applied to comprise the positive driven code pulse.

At the right-hand end of the track circuit, the operation of the track relay ZTR t it left-hand position as shown, causes the contacts of the relay 2CP to be actuated to their right-hand positions to apply a positive inverse code pulse from the transformer 26 through polar contact 25 in a right-hand position, positive rectifier unit 32, polar contact 23 in a left-hand position, variable resistor 23 to the track circuit 3-2T. The timing relay 2CPT is of course energized at the same time through positive rectifier 21 so that its polar contact 28 is actuated to the right to allow only one half-cycle of alternating current to be applied to the track circuit.

At the left-hand end of the track circuit, the inverse code pulse flows through contacts 38 and. 39 in right-hand positions to energize the inverse code track receiving relay 3TB to actuate its contact 29 actuated to a right-hand position.

It will thus be seen that driven code pulses of opposite polarities alternately are transmitted over the track section 32T so as to operate the track relay 2TB to its opposite positions. Similarly, inverse code pulses of opposite polarities a1- ternately are transmitted to the left over the track section 3-2T to operate the contacts of the relay 3TB to their opposite positions. It will also be observed that while a driven code pulse is being applied to the track circuit 3-2T, the track relay STR is disconnected from the track circuit by reason of the contacts 38 and 39 being out of corresponding positions, but as soon as the application of energy to the track circuit ceases, these contacts are in corresponding positions so that the track relay 3TB is connected across the track circuit in readiness for receiving the next inverse code pulse.

Similarly, at the other end of the track circuit, the track relay 2TB is normally connected across the track circuit by the contacts 35 and 36, but when an inverse code pulse is applied to the track cii-auitL-ZT; the track. relay Z'LRiis: disconnected.

therefrom until the inverse code pulse has been applied and the timing relay ZCPThas operated.

In this-way, the track relays are normally placed;

across the track circuit in readiness for receiving an impulse from-the opposite end of the track circuit, but are prevented from being energized by the transmission of an impulsefrom their respective ends of the track circuit by reason of being disconnected therefrom duringthe transmission of such impulse.

Thealtern-ate operation of the contact l of the track relay 2TB to its opposite positions is repeated into its repeating relay ZTRP' connected in multiplewith the relay 2C? so that the contacts 42 and: 43 of the relay ZTRP' are operated to their-opposite positions-in accordance with the 1801' code rate (or'ZScode rate as the case may be). Such operation energizes the decoding transformer 4'4 and acts to energize the home relay 2H in theusual well known manner. The circuit for the distant relay 2D is tuned for the 130 code and thus is energized as is well understood inthe art.

Thus, if a train opproacheson the track section- 2T causing the track rails to be-shunted and preventing the-reception of the inverse code pulses operating a relay ZFBP (not shown but similar to the relay 3FBP) then this relay ZFBP drops away to close a circuit for the green lamp G of signal 2. from. through a circuit including back contact 46. of relay ZFBP, front contact 41 of relay 2H, front contact 48" of relay 2D, green lamp G, to

Similarly, the passage of the train over the track section 3.--2-T prevents the reception of inverse codepulses by the track relay 3TB. causing a release of the relay SFBP, as previously described, and results in the energization of the proper lamp of the signal 3 as controlled by the relays 3H and 3D inaccordance with the trailic conditions in advance. It is obvious that with the train in the track section 3--2T, driven code pulses are not received by the track relay 2TB so that the relays 2H and 2D drop away, and any following train receives a stop signal by reason of. the closed condition of back contact 41 of relay 2H energizing the red lamp R of signal 2.

When the train passes into the track section 3T, the relays 3H and 3D are of course deenergized and the closure of back contact 12 of relay 3H connects the relay 3GP to the coding contacts 150T, so that the positive and negative driven code pulses applied to the track rails 3 2T are in accordance with a '75 code rate. This is received in the right-hand end of the track section 3--2T in a similar manner as previously described for the 180 code rate, but the contacts of the track repeating relay ZTRP being operated at the 75 code rate causes the energization of only the home relay 2H,. the relay 2D being responsive to code impulses of only the 180 code rate. Thus, any following train would receive a caution indication from signal 2 by reason of the energization of the yellow lamp Y of that signal.

It will be noted that the diagrams of Fig. 2 have been shown in connection with the application of impulses at the 180 code rate, the time involved for one complete 180 code rate cycle, that is, the usual on and ofi period of a 180 code, being of a second. This has been chosen because a slower code rate would consume more time for a complete code cycle period, and assuming an alternating current of a 60 cycle sine wave form, would mean that the diagrams would have to. be much smaller in. order to:be-.illustrated. on the usualPatent Oflice drawing sheet. However, it is believed that it will be readily understood by analogy, that codes. of difierent rates: than those shown and considered may be transmitted over a track section in accordance with the present invention. The contact response indicated for the relays named in Fig. 2 is not intended to show the position of such contactsbutto merely indicate the relative time of response.

In brief summary of the; disclosure of Fig. l, a code of any particular rate comprises a positive impulse and a negative impulse to mark the beginning of what is usually considered each on period and each} off period of the particular code rate then being transmitted. Instead of the inverse code being transmitted during only what is considered as an oflperiodin the usual coded track circuit organization, inverse code pulses immediately follow the driven code pulses. and the successive On and 01T- periods usually considered in connection with. inverse codes are overlapping in their: relationship tothe driven code periods in the present invention. This organization permits the transmission of inverse code pulses in a positive manner without any possibilityof over-lapping conditions. and perm-its very high driven code rates to betransmitted and still permit inverse codes to be reliably used in connection therewith.

With reference to Fig. 1, it will be seen that the transmitting relay 363? may continue in operation to. transmit driven code pulses although inverse code pulses are not being received. Thus, the track relay 3TB and the source of energy are alternately connected across the track section 32T. But. even if astray direct current potential is applied across the track rails of the track section 3-2T, for example, such potential merely actuates the contacts of the track relay 3TH to the position determined by the polarity of such potential. This is true in spite of the fact that the: supply of such stray current is intermittently interrupted by the operation of' the contacts of the relays. 3C]? and 3CP'I' included in the circuit for the. track relay 3TB. In other words, erroneous operation of the track relay 3TB is prevented in the presence of a stray direct current potential of either polarity because of the magstick type of relay employed. Thus, the inverse code of the present invention is inherently provided with a check against stray potentials across the: track rails which inthe usual systems may eliect. what has conveniently been termed as erroneous self-coding.

Apparatus of Fig. 3.--The principles of the present invention have also been applied to a stretch of track in Fig. 3 between two signal locations 5 and l governing trafiic in the same direc tion. This block between the signals 5 and I is divided into two track circuit sections 5'1 and ET by the usual cut. section. Such a cut section is usually provided when the block between signal locations becomes so long as to make it impractical to transmit code impulses the whole length of the block, and in such a case the block is divided by the so-called out section and the impulses from one section are repeated to the other by a source of current located at such cut section. A

. The track section 4T is in approach to the signal 5, while the track section IT is in advance of the signall. This stretch of track may be a portion of a double track railroad having the usual three-indication block signalling, or it may be a stretch of track immediately in approach to an interlocking plant. If the signal 1 is an automatic signal, then the home and distant relay 1H and ID will be automatically controlled in accordance with trainc conditions in advance by coded track circuit apparatus similar to that shown for the block between signals 5 and I, but if the signal I should be the home signal for an interlocking plant, then the home relay I would be manually controlled while the distant relay 1D would be automatically controlled in accordance with conditions in advance. This manual control for the home relay 7H would be such that the relay 1H would be normally deenergized to cause the signal 1 to remain at stop and place a suitable code on the track section GT in the rear of the signal. Also, if the signal I is a home signal in approach to an interlocking plant, then the approach relay 'IAR besides providing approach lighting control for the home signal, would also provide approach control for the interlocking to provide the usual well known approach looking for the switches of the interlocking plant.

Also if the signal 1 is a home signal for an interlocking, then the application of the inverse code to the track section 5T at signal 5 will be governed by the approach relay EARof the preceding approach track section 4T, but if these signals 5 and 1 are automatic signals of a double track roilroad, then the contact I! provided on the relay 5AR should be omitted from the circuit of relay 5GP so as to have the inverse code for the block between signals 5 and l originate at the signal 5, and to cease only upon the entrance of a train into the track section 5T.

In brief, the inverse code control disclosed in Fig. 3 may be employed for approach locking control as well as approach lighting control in view of the checked features of the inverse code as provided in the present invention, as will presently be described in more detail.

In this form of the invention, the code transmitting relays CP, the code transmitting timer relays CPT, and the track relays TR, are the same type of relays as employed in Fig. 1, namely, magstick type relays. These relays are a polarized type of relay having its contacts actuated to opposite positions upon the energization of the relay by current of opposite polarities, but the contacts remain in the last positions to which they are energized. However, these relays are shown in this form of the invention, as being controlled by direct current sources of energy, such as batteries, instead of by alternating current with rectifiers as shown in Fig. 1.

The apparatus at the signal locations 5 and 1 have been given the same letter reference characters as the relays shown in Fig. 1, but have distinctive preceding numerals associated therewith corresponding to the distinctive signal numbers, so that it will be easy to understand by analogy the similarity between the operation of this Fig. 3 and the operation pointed out in connection with the disclosure of Fig. 1.

At the cut section having insulated joints 59, the track relays BTRA and '5TRA are shown respectively associated with the track sections BT and ET, each relay providing for the repeat of impulses from its own track section into an adjoining track section by the control of the application of impulses from local track batteries 13 and 86 for the track sections ST and BT respectively. These relays have associated therewith the impulse timing relays 5CPTA and GCPTA for purposes presently to be described in greater detail.

These relays at the cut section 59 are also of the mag-stick type of relay.

It is believed that this form of the invention will be best understood by considering the detailed operation of the system.

Operation of Fig. 3.With reference to Fig. 3, it will be understood that contact 60 of relay 1H can be picked up or dropped away to selectively render either coding contacts ICT or T effective depending upon conditions previously described. In either case, the coding contacts in left-hand positions cause the polar relay 6GP to be energized from battery 51 in a direction to actuate its contacts to right-hand positions, and the coding contacts in right-hand positions cause the polar relay 6GP to be energized from battery 58 in a direction to actuate its contacts to lefthand positions. Under the conditions shown, no energy is supplied to the track circuits. The next actuation of the contact 6| of code transmitting relay 6GP to a left-hand position closes a circuit for applying negative potential from the battery 62 to the track section 6T through a circuit including contact 63 of relay BCPT. Such potential applied across the track section 6T causes current to flow through contact 64 of relay 5'I'RA in a left-hand position, and contact 65 of relay GCPTA in a left-hand position, through the Windings of the track relay GTRA at the cut section. This current flow is in such a direction that its polar contacts 66 and B1 are actuated to right-hand positions for applying negative energy to the section 5T through polar contact 68 of relay 5CPTA from battery 13.

But before considering the application of energy to the section 5T, it Will be seen that the polar timing relay BCPT is connected by polar contacts 70 and H across the track section 6T so that the energy applied to such track section 6T also causes current to flow through the windings of the relay GOP in a direction to actuate its polar contacts to left-hand positions. It is noted that the contact 10 is on this relay GCPT and opens its own energizing circuit, but a two-position magnetic stick type relay is of such a character that once its contacts are set into motion by energization of the relay windings, they will continue their stroke of operation even though the energizing circuit is broken. Thus, this relay BCPT operates a short interval after energy is applied to the track circuit ST and in so doing opens the connection for the negative portion of battery 62 to the track circuit at contact 63 and again connects the track relay B'IR across the track section through contact 63 in a left-hand position and contact 6| in a left-hand position. This timing relay GCP'I is designed to have such timing characteristic that it operates just slightly slower than the track relay GTRA, and thus measures the application of each negative and positive driven code impulse to the track section 6T so that it will be sufficiently long to allow for the proper operation of the code following track relay BTRA at the opposite end of the section. On the other hand, this relay BCPT is sufiiciently quick in its operation, the same as the track relay STRA, so that the driven code impulses need be of very short duration, in fact they are of substantially the same duration as required in Fig. 1, where a single half-cycle of 60 cycle commercial alternating current is of sufiicient duration to operate the relays properly.

It may also be noted at this time that this timing relay BCPT is operated to its opposite positions by the battery 62, the same source of energy which supplies the track circuit. Thus, if p the battery source is slightly above normal potential, then the relay GCPT will operate more quickly and this is proper inasmuch as the track relay BTRA will also operate more quickly. On the other hand, if the battery is slightly below normal, then the relay BCPT will operate more slowly and prolong the impulse period and thus give the relay [CPTA time in which to respond at the reduced potential.

Returning now to the cut section, it will be seen that, with contact 66 in a right-hand position and contact 68 in a left-hand position, the battery 13 supplies negative energy to the track section 5T, which negative energy flows through a circuit contacts 14 and 15 of relays 5UP and SCPT in left-hand positions and the track relay 5TB. in such a direction as to cause the track relay 5TB. to actuate its contact 16 to a right-hand position.

This reverses the direction of current flow in the track repeating relay 5TP and also in the code transmitting relay 5GP which includes front contact 11 of relay EAR.

It will readily be appreciated that the timing relay 5CPTA is supplied with current at the same instant that the battery 13 is connected across the section, so that energy flows through the windings of this relay 5CPTA in a direction for actuating its polar contacts to right-hand positions to open its own energizing circuit and to remove energy from track section 5T, the same as described for the relay GCPT.

The shifting of the polar contact 14 of the relay 5GP to a right-hand position in response to the reception of the negative driven code impulse, causes energy to be applied from the battery 36 through contact 8| of relay SCPT in a left-hand position to the track section 5T to form an inverse code pulse. The energy thus applied to the track section 5T also flows through contacts 82 and 83 to energize the timing relay 5CPT which operates its contacts to right-hand positions, opening its own circuit and disconnecting the battery 80 from the track section 5T to terminate the inverse code pulse. But this inverse code pulse is of suflicient duration to energize the track relay 5TRA through polar contact 66 of track relay GTRA in a right-handposition and polar contact 68 of relay 5CPTA in a right-hand position. The track relay 5'IRA then actuates its contacts 64 and '81 to right-hand positions. The operation of polar contact 64 of this track relay E'I'RA to a right-hand; position, closes a circuit through polar contact 85 to connect the battery 86 across the track section 6T to apply a negative inverse code pulse to that track section. The impulse timing relay SCPTA is of course receiving energy at the same time through polar contacts 81 and 88 so that its operates to open its own circuit at polar contact 88 in a righthand position, to open the circuit for the battery 36 at contact 85 in a right-hand position, and to connect the track relay BTRA across the track section GT in readiness for the next driven code pulse. This negative inverse code pulse however is of sufiicient duration and intensity to actuate the polar contacts of the track relay ETR. to left-hand positions.

It should be noted that this reception of the inverse code pulse as repeated from the section 5T into the section 6T actuates the contacts of the relay 6TB. before the next succeeding driven code pulse is applied to the track section 6T.

In other words, the application of a driven code pulse to the track section 6'1 by the operation of the relay 6CP,results in the repeating of that driven code pulse into the track section 5'1 and the return of an inverse code pulse through both of these track sections ST and 61 before the coding contacts IBIJCT or I5CT again move to its left-hand position.

When the transmitting relay GOP is operated to its right-hand position by energy received from battery 58 with the coding contacts IBiICT or 15CT in left-hand positions (as selected by contact 69 of relay II-I), a positive driven code pulse is applied to the track section 6T from the battery 62 with contact 6| in a right-hand position and contact 12 in a left-hand position. This of course disconnects the track relay GTR from the track circuit GT and connects the relay BCPT across the positive portion of the battery 62 by contacts H and 10 being out of correspondence. After a time measured by the relay GCPT, the contacts I0 and 12 are actuated to right-hand positions, the battery 62 being disconnected from the track circuit GT and the track relay 6TB then being connected. The operation of contact ID of course disconnects the relay GCPT from the battery 62 so that it is only temporarily energized.

The reception of the positive driven code pulse at the cut section flows through contacts 85 and 64 in right-hand positions in such a direction through relay GTRA as to actuate its polar contacts 66 and B1 to left-hand positions.

The operation of polar contact 66 to the left while contact 63 is in a right-hand position, disconnects the track relay 5TRA from the track circuit 5'1 and connects the positive portion of the battery 13 to the track circuit through polar contact 69 in right-hand position. Energy is also supplied to the timing relay 5CPTA through polar contacts 51 and 84 in out of correspondence positions. After a very short interval of time, the relay 5CPTA operates its contacts to left-hand positions, opening its own circuit at polar contact 84 in a left-hand position, disconnecting the positive portion of the battery 13 from the track circuit ST, and again connecting the track relay STRA to the track circuit ET in readiness for the reception of an inverse code pulse.

The positive driven code pulse is received at the right-hand end of the track circuit ST and flows through polar contacts M and BI in righthand positions and track relay 5TB, in such a direction as to actuate the track relay contact 16 to a left-hand position. This of course energizes the relays 5T1? and 5GP in such a direction as to actuate their contacts to left-hand positions by obvious circuits.

The operation of polar contact 14 to the left disconnects the track relay 5TB and connects the positive portion of the battery 39 across the track circuit 5T. Polar contact 8'2 in a left-hand position with polar contact 83 in a right-hand position also supplies energy to the timing rela 5CPI' from the positive portion of the battery through a circuit including polar contact 15 in a right-hand position and a polar contact 14 in a left-hand position. After a, short interval of time, the relay ECPT operates its polar contacts to the left disconnecting the battery 80 from the track circuit ST, and again connecting the track relay 5TB, across the track rails in readiness for the reception of another driven code pulse.

The reception of the positive inverse code pulse applied to the track circuit ET is of course received by the track relay 5TRA which shifts its nects relay BTRA from the track circuit BT and connects the positive portion of battery 86 across the track circuit and also energizes timing relay BCPTA, When relay SCPTA shifts its contacts to left-hand positions after a very short interval the battery 86 is disconnected from the track circuit and track relay STRA is again connected. The reception of the positive driven code pulse by the track relay B'IR actuates its polar contacts to the right. Thus, the transmission of a positive driven code pulse from the signal location 1 over the track circuit 6T, is repeated into the track circuit ET and an inverse code pulse of the same polarity is returned over the track circuits 5T and BT before the next negative driven code pulse is transmitted.

It is to be noted that all of the timing relays GCPT, GCPTA, 5CPTA and 5CPT operate with respect to the impulses applied to the track circuits, the same as described in connection with the relay SCPT. In brief, these relays receive energy momentarily upon the application of energy to the track circuit, so that they respond to take this energy oiT the track circuit as soon as a sufilcient amount of energy has been applied to properly actuate the track relay at the opposite end of the particular track circuits with which they are associated. Although the variable resistors have not been mentioned in connection with the track circuits, it will be seen that a variabl resistor is provided for varying the amount of energy supplied to the track circuit by its associated battery source. Thus, manual adjustment may be made in the amount of energy to be supplied to the track circuit, and this of course change the time of the track relay response. Another variable resistor is also included in the energizing circuit for each of the timing relays so that the amount of energy flowing to such relays may be manually varied in accordance with the response of the track relays so as to obtain proper operation.

In this way, the operation of the coding contacts is repeated into the code transmitting relay SCP and driven code pulses are transmitted in accordance with the particular rate of the coding contacts then selected, and these driven code pulses are of opposite polarities alternately thus operating the track relay 5'I'R at the opposite end of the block to its opposite positions in accordance with the particular rate of the COdiIlg contacts then selected. Associated with the track relay 5TH is means for transmitting an inverse code pulse fOllOWiIlg each driven code pulse, and these pulses are of opposite polarities alternately so that the track relay 6TB at the driven code transmitting end is operated to its opposite positions in accordance with the particular driven code rate then being transmitted. In this way, the track relay 5TB operates in accordance with the particular rate of the driven code and this is repeated into its repeater relay 5TP, which has polar contacts that act through the usual decoding apparatus to operate a relay 5H for any of the codes, but to cause the energization of the distant relay 5D only upon the reception of a driven code of the 180 rate.

At the signal location 1, the track relay 6TB operates through its polar contacts 90 and 9| to control an approach relay llAR. in the same manner as the usual home relay, such as relay 5H for example, so that it is energized upon the reception of the inverse code pulses irrespective of the rate of the driven code pulses then being transmitted. If the inverse code pulses are no longer 2,399,760 polar contacts 64 and 81 to the left. This disconreceived then the relay 'IAR drops away closing its back contact 92 to approach light the signal I in an obvious manner.

As above mentioned, th circuits of Fig. 3 show that the inverse code transmitted from the signal location 5 is controlled by front contact 11 of an approach relay BAR, which relay 5AR is assumed to be controlled in a similar manner as the relay IAR except that its control may terminate insofar as the governing of its inverse code is concerned at the next signal in the rear of the signal 5, or at a cut section immediately in the rear of signal 5, as the case may be. This control of the inverse code at the signal 5 b the contact ll has been illustrated so as to show that the inverse code may be controlled for approach locking zones and thus cause the relay TAR to drop away when a train is within a limited distance of the signal 5. However, it is to be understood that this contact 11 will not be required if the signals 5 and l are merely automatic signals in automatic signalling territory. a

This form of the invention also provides protection for the inverse code in that a stray direct current potential across the track rails fails to cause self-coding at the inverse code receiving points. This form of the invention also shows how the driven and inverse codes may be repeated past a cut-section for a block between two signals that are too far apart for a single track circuit. This repeat operation is effected in accordance with the present invention directly during each measured period for the driven code then being transmitted in such a way that there is no necessity for decoding the various codes at such a cut-section, thus making the system of the present invention more economical in the apparatus employed in accomplishing this feature.

It will also be seen that the impulse timing relays, such as relay GCPT, also determine the length of the impulse applied to the track circuit in accordance with the strength of the battery source supplying such current, and this is true for each of the transmitters for both driven and inverse codes. Each of these relays, such as relay BCPT, is connected into the track circuit organization in accordance with the present invention in such a manner that it is isolated from the impulses transmitted toward its location from the opposite end of the track circuit. In the form shown in Fig. 3, the relay BCPT, for example, is shown having a polar contact 10 controlling its own energizing circuit which serves to isolate it from the track circuit after each driven code impulse has been timed. However, this isolation of the timing relays from the track circuit so as to be unresponsive to impulses transmitted from the opposite end of the track circuit, may be accomplished in several different ways such as illustrated in Figs. 4 and 5, for example.

With reference to Fig. 4, it will be seen that the transmitting relay BCPT is connected across the positive or the negative portion of the battery 62 in accordance with the position of contact I00 of the transmitting relay BCP. In other words, the relay 6GP operates exactly as described in connection with Fig. 3, so as to cause driven code pulses to be applied to the track circuit GT, and each time the contacts of this relay shift to new positions, the contact l0!) acts to apply the opposite polarity of energy to the relay GCPT. Such a change in polarity of energization of the relay BCPT causes it to shift ,units I06 and I'I.

its contacts after, a short interval of time and out off the driven code pulse then being applied to the track circuit GT. and to also reconnect the track relay ETR. One difference in this form of control for the relay BCPT is that the relay is normally energized ,from the battery 62, but the relay ECPT is isolated from the track circuit 6T so that any impulses received over such track circuit to operate the track relay 6TB cannot possibly afiect any erroneous operation ofthe relay GCPT.

Similar control isprovided by contact IIlI of relay GTRA for the timing relay CPTA. It is noted that thistype of control for the timing relays is particularly adapted to the driven code transmitting end of a track circuit, and in the modified form of the invention shown in this Fig. 4 it is desirable to providea different control for the timing relays at the inverse code transmitting end of each track circuit.

For example, the relay BCPTA is connected across the track circuit, 6T by contact I02 to selectively include either the rectifier I03 or the rectifier I04. These rectifiers act to prevent any current flow through the relay GCPTA dueto energyapplied to the track circuit at its opposite end, but, when energy is applied to the track circuit by the shifting .of polar contact 64 of relay STRA, the polarity of the track potential with respectto the rectifier I03 or I04 then connected, is such as .to allow current flow through the relay GCPTAand cause it to time the. impulse then being applied to the track circuit 6T. 7

A similar controlling contact I05 is provided on therelay 501? with the associated rectifier In other words, this form of control for the timing relays BCPTA and .5CPT is preferably associated with the inverse code transmitting end. of each track .circuit.- The detailed operation of this form of the invention will not be discussed inasmuch as the operation described with regard to Fig. 3 is applicable to this form of the invention except as regards the operation of the timing relays abovedescribed.

Certain parts of'Fig. 3 have been omitted from this Fig. 4 for the sake of simplicity, but it is to be understood that this Fig. 4 Ban organization the same as Fig. 3. a

Similarly, Fig. 5 discloses another form of control for the timing relays, and this form has also been simplified by theomissionof certain parts of Fig. 3, which shouldbe considered as a part of the complete organization in which the positive portion of the battery 62 thus maintaining front contact I2I closed to normally connect the track relay STR across the track circuit6T.

Upon a shift of the polar contact I20 to an opposite positiomthe relay ISCPT is connected across the negative portion of the battery 62 so that current flows in an opposite direction throughthis timing relay. This causes its magprinciples of Fig. fi-are'employedr -In-this form of the invention, the timing relays BCPT 6CPTA ECPTA and SCPT are neutral type relays. The control for each of these timing relays, such as BCPT is exactly the same regardless of whether it is located at the driven code transmitting end of a track circuit or at the inverse code transmitting end of such track circuit. Thus, it is believed that a discussion of the operation of :such a relay in connection with the transmission of a driven code from the left-hand'end of the track circuit 6T will be suff cient for an understanding of the operation of the other timing relays.

. More specifically, the operation of therel'ay BC? in accordance with the coding contacts, of vcourse actuates the polarcontact I20 toitsopposite positions.

With the polar contact I20 in a right-hand position,'it is obvious that the timing relay 0CPT is normally energized'from the results in the netic flux to pass through zero, which results in the momentary dropping away of its contact I2I. During this momentary release of relay fiCPT back contact I2I connects the negative portion of the battery as selected by contact I20, across the track circuit 6'1, but immediately upon the picking up of the relay 6CPT the back contact I2I is opened thus terminating the driven code pulse and reconnecting through front contact I2I the track relay BTR to the track circuit 6T. It will be apparent that this same operation occurs upon each shift of the polar contact I20 to an opposite position. .In other words, the driven code pulse is of a duration measured by the time .in which the relay SCPT is dropped away upon a reversal of a magnetic flux in such relay. This is of course a veryshort interval of time.

The operation ofthe relay 0GP to its opposite positions by coding" contacts as above described, application of drivencode pulses of opposite ,polarities alternately to the track circuit BT which are received by the track relay 6TRA and which are transmitted through the track. circuit 5T into the track relay 5TB in an obvious manner. 'The. driven code pulses at the .cut section are timed by the relay 5CPTA by thereversalof the direction of current flow through such relay. "The transmission of inverse code pulses is of course accomplished in a similar manner, and the inverse code pulse transmitted from he signal location 5 is of course received at the signal location I before the next driven code pulse is applied. This can be accomplished because of the very short duration of the driven and inverse code pulses.

' 'It'is to be understood that varidusmodifications may be made to the embodiments of the present invention and still come within the scope of the invention. For example, the code transmitting relays, such as relay 3GP of Fig. 1 or relay BOP of Figs. 3, 4 and 5, may be neutral relays instead of the mag-stick type relays shown providing a proper adjustment of the relays is made with respect to the coding contacts so as to obtain a'uniform timing operation. A mag-stick relay usually operates to its opposite positions uniformly, while a, neutral relay is usually slower releasing than it is in picking up. Thus, the presentembodiment has illustrated the use of a mag-stick relay in this connection, because it is desirable to have the periods during which the relay contacts are inits opposite positions as nearly uniform as possible.

Also, the Fig; 1 does not show a repeating organization at a cut section, but it is to be understood that the invention may be applied to a cut-section for such form of the invention in a similar manner as pointed out in connection with Fig. 3 using direct current, or if desired alternating current may be employed using connections similar to those shown in Fig. 1 for the transmitting and receiving ends of the track circuit shown.

Also, the code transmitting relay 2GP of Fig. 1 may be controlled by the contact of an approach 1 relay, such as relay EAR shown in Fig. 3, if the application of the invention to conditions of practice require such control (indicated by a in the drawings). 1

Having described a codedtrack circuit signalling system employing alternating current half-Waves for transmitting driven and inverse codes, as one specific embodiment of the present invention, it is desired to be understood that this form is selected for the purpose of facilitating the disclosure of the inverse rather than to limit the number of forms which the invention may assume, and it is to be further understood that various modifications, adaptations, and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention except as is limited by the appended claims.

What I claim is:

1. In a coded track circuit signalling system for railroads, a section of railway track, means at one end of said section for applying to the rails thereof single half-cycles of alternating current of opposite polarities alternately at diiferent selected time-spaced intervals in accordance with traflic conditions, a polarized code following track relay of the two-position type connected across the rails of the section at the opposite end, and decoding means controlled by said track relay and distinctively responsive to the difierent timespacing of said alternating current half-cycles.

2. In a, coded track circuit signalling system for railroads, a section of railway track, a source of alternating current at one end of said section, transmitting means at said one end for r'nomentarily connecting said source across the rails of said section to apply a single half-cycle of alternating current, said means acting to apply a suc cession of half-cycles of alternating current of opposite polarities alternately at diiferent selected code rates, a, two-position polarized track relay connected across the rails at the opposite end of said section, and decoding means controlled by said track relay distinctively in accordance with the different rates at which said track relay is operated.

3. In a coded track circuit signalling system for railroads, a stretch of railway track divided into sections by signals located at intervals along the stretch for governing traflic in a particular direction, means associated with the exit end of each section for applying to the rails at that end a single half-cycle of alternating current at successive time-spaced intervals reoccurring at a relatively slow rate, said relatively slow rate being any one of a plurality of different rates selected in accordance with traflic conditions for the section in advance, and said half-cycles being alternately of opposite polarities, and decoding means at the entrance end of each section for distinctively controlling the associated signal in accordance with the different rates of reception of said alternating current half-cycles.

4. In a coded track circuit signalling system for railroads, a' stretch of railway track divided into blocks by signals for governing trafiic in a particular direction, a source of alternating current at the leaving end of each of said blocks, means associated with the leaving end of each block for applying to the rails of that section at time-spaced intervals a half-cycle of alternating current from the associated source, said time-spaces being of diiferent selected durations in accordance with traflic conditions in the block in advance, and the successive half-cycles being of opposite polarities alternately, a polarized two-position code following track relay connected across the rails at the entrance end of each block, decoding apparatus governed by each track relay and distinctively controlled in accordance with the difierent time-spacings of said alternating current half-cycles, and means for controlling the indications of the associated signal by said decoding means.

5. In a coded track circuit signalling system for railroads, a section of railway track, a source of alternating current and a two-position polarized track relay at each end of said track section, means at one end of the track section for alternately connecting said source and said track relay across the rails of said section at that end at different selected code rates in accordance with trafiic conditions, said means being effective to apply only a single half-wave of alternating current to comprise a driven code pulse for each connection of said source to the rails and the successive driven code pulses being of opposite polarities alternately, means at the opposite end of said track section for normally connecting the track relay at that end to the track rails of the section so as to be responsive to the driven code pulses of alternate polarity applied to the track rails at said one end, said means acting in response to each operation of said track relay for momentarily disconnecting that track relay and connecting the alternating current source at that end across the track rails to supply a single half-cycle of alternating current to comprise an inverse code pulse, the successive inverse code pulses for successive operations of the associated track relay being of opposite polarities alternately to thereby operate said track relay at said one end of the section to its opposite positions, and means at said other end of said track section distinctively controlled by the track relay for that end in response to the different rates of operation of its contacts.

6. In a coded track circuit signalling system for railroads having time-spaced driven code pulses transmitted over a section of railway track, a two-position polarized track relay intermittently connected across the track rails at the driven code transmitting end between the successive driven code pulses, means at the opposite end of said track section responsive to each driven code pulse for applying an inverse code pulse during each time space between successive driven code pulses, said means causing the successive inverse code pulses to be of opposite polarities alternately t thereby operate said two-position polarized relay to its opposite positions, and means at said one end of said track section distinctively controlled only by the continued operation of said polarized relay to thereby indicate the presence of said inverse code pulses, whereby the erroneous energization of said track section with steady energy of either polarity cannot cause the operation of said two-position polarized relay and falsely indicate the presence of an inverse code.

'7. In a coded track circuit signalling system for railroads, a section of railway track, a twoposition polarized track relay and a source of energy located at one end of said section, means at said one end for alternately connecting said relay and said source of energy across the track rails of the section, said means acting to apply pulses of opposite polarities alternately to the track rails of the section for the successive connections of the source to the rails, a two-position polarized track relay normally connected across the rails of the section at the opposite end, means responsive to each operation of said track relay at such opposite end for temporarily disconnecting that track relay from the rails and applying an inverse code pulse to. the, track rails, the .successive inverse code pulses for successive operations of the track relay being of opposite polarities alternately, to thereby operate said track relay at said one end to its opposite positions,

whereby the presence ,of a foreign current across the track rails of either polarity cannot cause the alternate operation of said track relay at said one end even though such track relay is being intermittently connectedand disconnected from the rails of the track section.

8. In a coded track circuit signalling system for railroads, a section of railway track, a two-position polarized relay and a source of energy at one end of the section, code transmitting means for alternately connecting said polarized relay and said source of energy across the track rails of the section at different time spaced intervals in accordance with traific conditions, a track relay at the opposite end of the track section responsive to the successive energizations of the track rails by said code transmitting means, means distinctively controlled by said track relay at said other end in accordance with its different rates of operation, inverselcode transmitting means associated, with said otherend of said track section for applying an inverse codepulse during the time space following the reception of each driven codepulse said means actingto cause the successive inverse code pulses to be of opposite polarities alternately to thereby operate the two-position polarized relay at. said, one end of the track section to its opposite positions, means at said one end ,of saidtrack section distinctively controlled byits associated two-position polarized relay only upon the continued operation of such polarized relay to its opposite positions, whereby the presence of a steady foreign current on said tracksection of either polarity failsto cause the intermittent and alternate operation of said two-position polarized relay although said driven code transmittingmeansis operated.

9. In a coded track circuit signalling system for railroads, a stretch of railway track between entrance and exit signal locations divided into two track circuit sections by insulated joints in an intermediate cut section, a track relay and a source of energyat each end of the, track circuits, driven code transmitting means at the exitend of the stretch for alternately connecting. said track relay and said source at that end across the track rails of the associated track circuit tothereby transmit driven code pulses at difierent selected code rates in accordance with trafiic conditions in advance, repeating means associated with each' track relay at the cut section and controlled thereby while that relay is energized by a code pulse received over the rails of its respective track circuit for disconnecting the track relay for the adjacent end of the adjoining track'circuit from .the rails thereof and then momentarily connecting theassociated source, means at the entrance end of saidstretch responsive to each operation of the track relay at that end for momentarily disconnecting such track relay from the rails' and momentarily connecting the associated source of energy to apply an inverse code pulse,

means at the entrance endor said stretch responsive to the operation of the corresponding to govern the indications of the entering signal track relay at the difi'erent code rates for controlling the indications of the associated signal, and means at the exit end of said stretch controlled by the continued operation of the track relay at that end in response to the inverse code pulses repeated past said out section by said repeating means.

10. In a coded track circuit signalling system for railroads, a stretch of track between entrance and exit signal locations divided into two track circuit sections by an intermediate out section, a track relay and a source of energy at each end of the trackcircuits, said track relays being normally connected across the rails of their respective track circuits, code transmitting means at the exit end of said stretch for intermittently disconnecting. the track relay at that, end and momentarily connecting the associated source of energy for transmitting driven code pulses at different selected code rates in accordance with traffic conditions in advance, means at the cut section for each track relay associated with said out section effective during the energization of that track relay to disconnect the track relay of the adjoining section from the rails thereof and mementarily connect the associated source to repeat a code pulse from one track circuit section into the other for either direction of transmission, means at the entrance end of the stretch momentary connection of the associated source across the rails to transmit an inverse code pulse, and meansat the exit end of the stretch responsive to the operation of the track relay at that end by the inverse code pulses to control the approach lighting of said exit signal, whereby driven and inverse code pulses are directly repeated past a cut section.

11. In a codedtrack circuit signalling system for railroads, a stretch of track between two signal locations divided into two track circuits by an intermediate cut section, a two-position polarized relay and a source of energy at each end of each of the track circuits, said polarized relays being normallyconnected across the track rails of their respective track circuits, driven code transmitting means at the exit end of the stretch for disconnecting said track relay and connecting said source of energy across the track rails of the section atdifferent code rates, each of said connections being relatively short and so effected as to cause alternate pulses to be of opposite polarities, means associated with each track relay atthe cutsectionand responsive to each op- ,mita relatively short pulse, said means being so organized as to cause alternate pulses to be of opposite polarities, means at the entrance end of the stretch responsive to the operation of the track relay at that end to its opposite positions in accordance with the different driven code rates for governing the passage of traific into said stretch, means responsive to each operation of the track relay at said entrance end to its opjposite ,position's tor temporarily disconnecting that track relay and momentarily connecting its associated source across the track rails of its section to transmit an inverse code pulse, said means being so organized as to cause alternate inverse code pulses to be of opposite polarities, and means controlled only by the continued operation of the track relay at the exitend of the stretch to its opposite positions alternately, whereby driven and inverse codes of opposite polarities alternately are directly transmitted past an intermediate cut section.

12. In a coded track circuit signalling system for railroads having a plurality of track sections each having driven code pulses transmitted in one direction and inverse code pulses of opposite polarities alternately transmitted in the opposite direction, a code transmitting and receiving means for the exit end of each section comprising, a track relay of the two-position polarized type, a source of energy, a transmitting relay operable to its opposite positions at any desired code rate, a two-position polarized timing relay, circuit means for operating said timing relay to an opposite position upon each operation of said transmitting relay to an opposite position, said means energizing said timing relay from said source, and means including contacts of said transmitting relay and said timing relay to normally connect said track relay across the rails of a track section but acting upon each operation of said transmitting relay to disconnect said track relay from said rails and momentarily connect said source across said rails until said timing relay is operated.

13. In a coded track circuit signalling system, a code transmitting and receiving means comprising, a track relay, a source of energy, a transmitting relay operated to its opposite positions in accordance with different selected code rates, a two-position polarized timing relay operated to an opposite position upon each operation of said transmitting relay by energy supplied from said source, means for disconnecting said timing relay from said source upon each operation of said timing relay, and means acting while said transmitting and timing relays are in corresponding positions for connecting said track relay across the rails of a track section but acting while they are out of corresponding positions to disconnect said track relay and connect said source, whereby said source is intermittently connected across the track rails at a rate corresponding to the rate of operation of said transmitting relay to thereby transmit driven code impulses, and whereby the duration of each impulse transmitted by the connection of said source across the rails is measured by a timing relay energized from the same source that supplies the impulse energy.

14. In a code transmitting and receiving means for a coded track circuit, a code transmitting relay, a two-position polarized track relay, a neutral timing relay, a source of energy circuit means eiTective to normally energize said timing relay from said source but acting upon each operation of said transmitting relay to reverse the direction of current flow through said timing relay, whereby its contacts are momentarily released, circuit means for connecting said track relay across the rails of a track section while said timing relay is picked up, and means for disconnecting said track relay from said rails and connecting said source across said rails while said timing relay is released.

15. In a driven code receiving means and an inverse code transmitting means for coded track;

circuits used on railroads, a track relay of the two-position polarized type normally connected across the track rails of a coded track circuit having driven code pulses of different selected rates applied thereto the successive code pulses being of opposite polarities alternately, a twoposition polarized timing relay, a source of energy, circuit means effective upon each operation of said track relay to disconnect itself from the rails of said track section and connect aid source across said rails and at the same time energizing said timing relay to an opposite position, said circuit means acting to disconnect said source and reconnect said track relay across the rails when said timing relay has operated in response to the operation of said track relay, and said circuit means being organized to cause said source to supply energy of opposite polarities alternately upon successive operations of said track relay, and means including rectifier Lmit acting upon said circuit means with respect to said timing relay for preventing energization thereof by driven code pulses received over said track rails.

16. In a driven code receiving means and an inverse code transmitting means, a two-position polarized track relay connected across the track rails of a track circuit receiving driven code pulses of different selected rates the successive pulses of which are of opposite polarities alternately, a timing relay of the two-position polarized type, a battery source, circuit means including contacts governed by said track relay and contacts of said timing relay for connecting said timing relay to said source upon each operation of said track relay by a driven code pulse to energize said timing relay in a direction causing it to operate its contacts to an opposite position and thereby disconnect itself from said source, circuit means effective upon each operation of said track relay for disconnecting itself from said rails and connecting said battery source, said means acting upon operation of said timing relay to disconnect said battery source and reconnect said track relay, and said means also including contacts causing said battery source to be connected to supply energy of opposite polarities alternately for successive operations of said track relay, whereby said timing relay is actuated to its opposite positions by energy supplied in accordance with the potential of said battery source to thereby provide inverse code pulses of a duration commensurate with the potential of such source, and whereby said timing relay is unresponsive to the driven code pulses acting upon said track relay.

17. In a driven code transmitting means for coded track circuits, a transmitting relay operated to its opposite positions in accordance with different selected code rates, an alternating current source of energy, a two-position polarized timing relay, circuit means acting upon each operation of said transmitting relay to connect said alternating current source across the rails of a track section, circuit means controlled by said transmitting relay for energizing said timing relay in a direction to actuate its contacts to an opposite position upon each operation of said transmitting relay within a time period substantially equal to only a single half-cycle of altemating current, and means acting upon the operation of said timing relay following the operation of said transmitting relay to disconnect said alternating current source from said track rails, whereby driven code pulses are transmitted each comprising a single half-cycle of alternating current.

18. In a driven code transmitting apparatus for coded track circuits, a transmitting relay operated to its opposite positions at difierent selected code rates, an alternating current source of energy, a two-position polarizedtiming relay, circuit means controlled by said transmitting relay for energizing said timing relay in an opposite direction upon each operation of said transmitting relay, two rectifier units, circuit means for connecting said source of alternating current acoss the rails through one of said rectifier units when said transmitting relay has operated to one position and said timing relay is energized but has not yet actuated its contacts to a corresponding position, and other circuit means for connecting said source across the rails through said other rectifier unit when said transmitting relay has operated to the other position and said timing relay is energized but its contacts have not yet operated to such a corresponding position, said timing relay acting in response to its energization to move its contacts to opposite positions into correspondence with said transmitting relay Within a time suificient to allow only a single half-wave of alternating current to be applied to said rails, wherebydriven code pulses are transmitted over the rails of a track circuit each comprising a single half-cycle of alternating current and the successive driven code pulses being of opposite polarities alternately.

19. In a coded track circuit organization for a section of railway track, a source of energy at one end of said section, a transmitting relay at the corresponding end operating intermittently in accordance with the different selected code rates, a timing relay operated upon each operation of said transmitting relay by energy supplied from said source to thereby be operated an interval of time following each operation of said transmitting means depending upon the existing potential of said source, circuit means including contacts operated by said transmitting and timing relays for initially connecting said source across the rails of said track section upon each operation of said transmitting relay but disconnecting said source upon the following operation of said timing relay, whereby said source is intermittently connected across the track rails at a rate corresponding to the rate of operation of said transmitting relay and for a duration measured by the operating time of said timing relay as determined by the existing potential of said source of energy, a track relay connected across the rails of the other end of said section, and decoding means controlled by said track relay, whereby the amount of energy transmitted to said track relay remains substantially the same for each code pulse regardless of variations in the potential of said source.

20. In a coded track circuit organization for a section of railway track, a source of energy at one end of said section, a transmitting relay at that end intermittently'operated at different selected rates, a timing relay, circuit means acting to energize said timing relay from said source following each operation of said transmitting relay, circuit means including contacts operated by said transmitting and timing relays for connecting said source across the rails of said track section upon each operation of said transmitting relay and disconnecting said source upon the following operation of said timing relay, said circuit means acting to connect said source with opposite polarities alternately for the successive connections to the rails, a two-position polarized track relay connected across the rails at the other end of said section, and decoding means responsive only to the alternate operation of said two-position polarized track relay, whereby said two-position polarized track relay is operated to opposite positions alternately by the successive code pulses applied to said rails from said source, and whereby the amount of energy transmitted to said twoposition polarized track relay for each code pulse remains substantially the same regardless of variations in the potential of said source since the time interval of each connection of the source across the rails depends upon the potential of said source as applied to said timing relay.

FRANK X. REES. 

